1. Field
One embodiment of the invention relates to a disk drive using a disk medium storing servo information and, in particular, a head positioning control technique using spiral servo information.
2. Description of the Related Art
Generally, in disk drives typified by hard disk drives, servo information used for control of positioning the head (servo control) is recorded on a disk medium being a data recording medium. In disk drives, the head is positioned to a target position (target track) on the disk medium, using the servo information read by the head.
The head performs writing of data or reading of data in the target position. Generally, the head is separated into a read head and a write head, and the read head reads data (including servo information), and the write head writes data.
The servo information recorded on the disk medium is generally recorded on servo sectors, which are circumferentially arranged at regular intervals, and the servo sectors form concentric servo tracks. In disk drives, the head positioned on the basis of servo information records user data in concentric data tracks formed on a disk medium.
In the meantime, proposed is a disk drive using a disk medium recording spiral servo information, not concentric servo information, in manufacturing process of disk drives to improve the efficiency of a servo writing step of recording servo information on a disk medium (for example, refer to Jpn. Pat. Appln. KOKAI Pub. No. 2005-32350). In this technique, the efficiency of the servo writing step is improved in comparison with the case of using concentric servo information, because writing spiral servo information requires no head stop time, and thus servo information is written on the whole surface of a disk medium for a relatively short time.
On the other hand, in commercialized disk drives, it is required to write user data (computer data and stream data such as images) in a concentric data track on a disk medium. This is because concentric data tracks have higher random access efficiency than that of spiral tracks.
However, when servo information is read from a spiral servo track and positioning of the head is performed with respect to a concentric data track, the track center line of the servo track is shifted from that of the data track, and without any measures the head positioning accuracy deteriorates. Therefore, the efficiency of positioning control operation deteriorates, and consequently random access performance to concentric data tracks deteriorates.